But on a hot July afternoon in Chicago, on a footprint where tracks once visibly sliced through a great American city, a skinny couple cavorts on the verdant lawn of Pritzker Pavilion. He has his shirt off. She lies lazily, happily on the grass, her face covered by her Sox cap, her body arched. He kisses her stomach. They are, like all summer lovers worth their salt, oblivious to their surroundings.

Great urban parks — and, 10 years after its creation, Millennium Park is making a fine case for nomination into that category — offer spaces for privacy and intimacy, an ecumenical illusion, at least, of escape from the throb of the metropolis. Yet in its first weeks of existence, people walked through Millennium Park with a palpable air of deference.

Chicagoans knew they were lucky to have this curated, arty place — built, at eye-popping cost, by a remarkable, pre-pension-crisis, pre-recession collision of mayoral will, urban-suburban cohesion and philanthropic means. But they mostly walked within its boundaries gingerly, keeping off the grass, admiring the high-end artworks and gardens, unsullied by sweet corn from Taste of Chicago, so near and yet so far away. There was much talk of what kind of concerts would be allowed, which bands, which audiences, would be kept at bay. Millennium Park felt pristine, Apollonian, admirable but not really of the people.

It was policed — benignly, but still policed — by officers on Segways. They looked ridiculous, but they had rules. They felt like the enforcers of the ethos of the park's founders, whose names were inscribed ("for all time") on the pretentious classical structure, the Millennium Monument, at the park's northwest entrance. Thanks to the immortalized founders, the park opened July 16, 2004.

Ten years on, Millennium Park has come into its own by becoming a whole lot messier.

It has found a new willingness to embrace some mild bad behavior from those who seek solace in its boundaries. Just as crucially, it has allowed some of its own imperfections to show. Bald spots now pockmark its once-pristine grasses. The carefully coded map at its entrance has water damage at the edges of the sign. Railings dividing the park areas now are covered in weeds. Millennium Park is a little less perfect and a whole lot more comfortable to visit.

Millennium Park is filled with activities for visitors from yoga on the Great Lawn, to sculptures from China and gourmet treats. They can dress up, take part or watch the show.

And visit they do. Millennium Park has become the crossroads of the city, the intersection of North and South, a place shared equally by locals and tourists, a raiser of bars across all of cultural Chicago, a reminder of how the high-end and the populist can and should be one and the same.

On this gorgeous summer day, you can watch kids walking walls. You can see a homeless guy with two suitcases and a plastic Walgreen bag. A couple speaking Japanese sit on a bench, his leg snaked under hers. A kid clutches a toy zebra. Two young women tote skateboards.

You might hear a snatch of conversation ("I was in eighth grade when …"; "It's so great to see you guys together.").

A guy in a Brazil shirt laughs uproariously, not knowing what would befall his soccer-loving nation within 24 hours. At the Bean (who calls it anything else?), thousands of shots destined for Facebook compete with three professional crews, each filming something about Chicago for someone, somewhere.

Millennium Park has become a 'nexus for tourists and residents' in Chicago.

Millennium Park has become a 'nexus for tourists and residents' in Chicago.

Kids wearing Gage Park T-shirts stare at a sign: "The waterfront by right belongs to the people." A woman holds up a tablet to take a photo of the giant head sculpture, staring West, not South nor North. The iPad has a crack, but it's not debilitating.

A Tibetan monk wanders through the gardens. A man in a zoot suit sits on the grass. A girl in pink shiny shoes stares as her mom sells M&Ms from a big box. The place feels safe yet cosmopolitan, familiar but grand, diverse — no buts about that.

What has been achieved here? Well, the two signature attractions for the casual visitor — Crown Fountain and the Bean — were, in so many ways, perfectly designed for the new experiential, touch-obsessed moment. The Bean has turned out to be the ultimate smartphone-friendly destination, its shiny surface offering so many chances for the self-chronicler, its reflective surface offering a selfie within a selfie within a selfie, and beloved for that. Outside the fountain on Michigan Avenue, buses roll by with advertisements for the Museum of Science and Industry and Shedd Aquarium. These consultant-tested ads tout interactive experiences to parents felled by electronic devices. Millennium Park, though, has never really needed to advertise. Its experiential qualities are impossible to miss.

At the fountain, which finds its best moments as dusk and more teenagers arrive to find some useful calm in its benign waters, people frolic in a not-quite-a-water-park space, where the semi-illicit ways to get wet are part of the fun. Nobody cares much about the aging video towers anymore — they're too busy ignoring the sign that tells you not to run, a posting that seems more like artwork than an actual rule.

Toddlers splash. Teenagers soak themselves, their clothing clinging to their bodies. The space can be enjoyed at whatever level of transgressive commitment matches your comfort level. If you were there when Millennium Park opened, all of this is so very hard to believe.

Millennium Park ennobles everyone, which is the ultimate accolade for a public space. It has few credible detractors. It has made public spaces that do not live up to its standards appear subpar and in need of renovation; in many cases, they've had no choice but to improve. It has done a city a favor. It has spawned condos and new coffee shops. It has centered a community.

Millennium Park has done all this with no reliance on tradition and without much of an entrance — no grand gates like those of London's Hyde Park, no benefiting from a city that grew up with a park already at its core.

Millennium Park was more of a retrofit, really. Visitors come upon it on the regular city grid, which makes it all the more surprising. But stand at its heart, and you'd swear the great skyscrapers on Randolph Street were built to take advantage of its design. They each seem to rise with purpose, sharing its materials, drawing from its roots.

Those roots, when you think about it, have barely taken hold. Ten years is nothing, and it went by in a blink. Millennium Park, though, is something that plays in the city that works, a fun spot, a classy joint, a place where locals proudly take visitors and are empowered when they arrive.